Brake system and method

ABSTRACT

A hydraulic system for an aircraft includes a brake operation device, a pressure supply, a reservoir, a shut-off valve, and a wheel brake. The shut-off valve is in fluid communication with and is disposed between the pressure supply and the brake valve. The shut-off valve can include a poppet, a first valve seat and a second valve seat. Movement of the poppet is controlled by operation of the brake operation device. The poppet is movable between a first position where the poppet acts against the first valve seat and a second position where the poppet acts against the second valve seat. In the first position, fluid flow is blocked between the pressure supply and the brake valve through the shut-off valve. In the second position, fluid flow is allowed between the pressure supply and the brake valve through the shut-off valve. The wheel brake is in fluid communication with and downstream from the shut-off valve.

BACKGROUND

This disclosure is related to a brake system of an aircraft.

Hydraulic systems in mid and large size aircrafts are used in primarysystems such as flight control systems. In the mid and large sizeaircrafts, engine driven hydraulic pumps and the like are used as ahydraulic pressure source, because double or more hydraulic systems areneeded to be used with the primary systems and the hydraulic systems areused at all flight times in mid and large size aircrafts. In theseaircrafts, a quantity of fluid leakage in the hydraulic system is notcontroversial, because the hydraulic pumps are activated at all times inthe aircrafts and the hydraulic pressure does not decrease because ofthe leak.

On the other hand, hydraulic systems in small business jet aircrafts areused with secondary systems like landing gear control, brake, steering,speed brake and the like in general. Therefore, in the small businessjet aircrafts, hydraulic pressure source is only used in a short amounttime during a flight. Especially, the hydraulic pressure source is notnecessary at all during cruise, though cruise time is a large share offlight time. That is, hydraulic systems driven by electrical pumps areoften employed to produce hydraulic pressure at the time of need only.

Typically, small business jet aircraft have also a pressure accumulatoras a system redundancy device in preparation for failure of thehydraulic pressure pumps and the like. In the event of a pump and/orelectrical system failure, accumulators hold hydraulic fluid volumeenough to stop the aircraft on the ground. In this instance, thequantity of internal leakage in the hydraulic system is very important,because the volume size of the accumulator is decided with considerationof the internal leakage. Furthermore, a large amount of leakage canrequire the electrical motor driven pump to turn off and on frequently.Turning the electrical pump on and off frequently reduces the life ofseveral components including the electrical motor, the hydraulic pump,hydraulic system parts, as well as electrical power generator system.

Recently, the number of small business jet aircrafts that are providedwith power brake systems including a metering-pin valve and providedwith anti-skid brake systems are increasing. Usually, a servo-valve isused in the anti-skid brake system, because anti-skid brake systemshould release brake pressure at once to realize the anti-skid function,and servo-valve is suitable for this performance. Typically, acombination of jet-nozzle and flapper-valve is used in the servo-valve.However, the quantity of internal leakage from the metering-pin valveand the servo-valve is not negligible due to the characteristic featuresof these valves.

There can be found infrequently that small business jet aircrafts havingan electromotive drive shut-off valve which is upstream of the brakemetering valve and the anti-skid valve. Electronic solenoids can be usedto drive the shut-off valve. The quantity of internal leakage from thatkind of shut-off valve is not negligible too. In addition, whenelectrical power is not provided to that kind of shut-off valve, thebrake system goes out of control. Furthermore, hydraulic pressure spikesare created by the electromotive drive shut-off valve, becauseconditions of on and off of the electromotive drive shut-off valve arealways switched immediately. The hydraulic pressure spikes, which areprovided to the hydraulic system, brake system and landing gear systemof the aircraft, cause large acoustic noise and affect lifespan of thehydraulic system and the like.

SUMMARY

A hydraulic system for an aircraft includes a brake operation device, apressure supply, a reservoir, a shut-off valve, and a wheel brake. Theshut-off valve is in fluid communication with and is disposed betweenthe pressure supply and the brake valve. The shut-off valve can includea poppet, a first valve seat and a second valve seat. Movement of thepoppet is controlled by operation of the brake operation device. Thepoppet is movable between a first position where the poppet acts againstthe first valve seat and a second position where the poppet acts againstthe second valve seat. In the first position, fluid flow is blockedbetween the pressure supply and the brake valve through the shut-offvalve. In the second position, fluid flow is allowed between thepressure supply and the brake valve through the shut-off valve. Thewheel brake is in fluid communication with and downstream from theshut-off valve. The wheel brake operates at a maximum fluid pressure andthe wheel brake is at x % of the maximum pressure when the poppet is inthe second position, where x %<100%.

A method for operating a brake system includes depressing a pedal tomove a poppet in a shut-off valve from a first position toward a secondposition. When in the first position the poppet blocks fluid flowbetween a pressure source and a brake valve. When in the second positionthe poppet allows fluid flow between the pressure source and the brakevalve. A wheel brake, which is connected with the shut-off valve, is atx % of a maximum brake pressure when the poppet is in the secondposition. The method further includes further depressing the pedal withthe poppet in the second position to provide a brake pressure greaterthan x % in the wheel brake.

An example of a shut-off valve that can overcome at least some of theshortcomings mentioned above includes a housing, a first valve seat, asecond valve seat, a spool, a poppet, a first piston, and a firstspring. The housing can include a bore, a master cylinder port, apressure supply port, a system pressure port, and a return port. Eachport can connect with the bore, and the bore includes a valve seatsection and a piston receiving section. The valve seat section isconnected with the system pressure port, and the piston receivingsection is connected with the return port. The first valve seat isdisposed in the valve seat section of the bore between the pressuresupply port and the system pressure port. The second valve seat isdisposed in the valve seat section of the bore between the systempressure port and the master cylinder port. The spool can be disposed inthe bore. The poppet is on the spool, and the poppet can move with thespool. The poppet is disposed in the valve seat section for movementbetween the first valve seat and the second valve seat. The first pistoncan be disposed in the piston receiving section of the bore and connectwith the spool for movement with the spool. The first spring is disposedin the piston receiving section of the bore and biases the first pistonand the poppet in a first direction towards the first valve seat. Whenpressure at the master cylinder port overcomes a biasing force of thefirst spring and pressure at the return port, the first piston and thepoppet travel in a second direction.

A hydraulic system for an aircraft that can overcome at least some ofthe aforementioned shortcomings includes a master cylinder, a wheelbrake, a pressure supply, a reservoir, and a shut-off valve incommunication with the master cylinder, the wheel brake, the pressuresupply and the reservoir. The shut-off valve can include a seal that isconfigured to preclude fluid flow between the pressure supply and thereservoir through the valve. The shut-off valve can be operable in afirst position which blocks fluid flow between the pressure supply andthe wheel brake through the valve and a second position which allowsfluid flow between the pressure supply and the wheel brake through thevalve. Fluid pressure from the master cylinder can control operation ofthe valve between the first position and the second position. Failure ofthe seal can result in fluid flow from the brake pressure supply towardthe master cylinder.

Another example of a shut-off valve includes a housing, a spool, apoppet, a valve seat, a seal, a first piston, and a second piston. Thehousing can include a bore, a master cylinder port, a pressure supplyport, a brake pressure port, and a return port. Each port can connectwith the bore. The spool can be disposed in the bore. The poppet can bedisposed on the spool, and the poppet can move with the spool. The valveseat can be disposed in the bore between the pressure supply port andthe brake pressure port. The poppet can seal against the valve seat toblock fluid flow through the bore from the pressure supply port towardthe brake pressure port. The seal can cooperate with the spool and thehousing to block fluid flow through the bore from the pressure supplyport and the brake pressure port toward the master cylinder port. Thefirst piston can be disposed in the bore and connected with the spoolfor movement with the spool. The second piston can be disposed in thebore. The second piston can include a second piston passage thatreceives the first piston. The first piston can cooperate with thesecond piston to block fluid flow through the bore from the mastercylinder toward the return port. The second piston can cooperate withthe housing to block fluid flow through the bore from the mastercylinder port toward the return port.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic depiction of a hydraulic brake system for anaircraft.

FIG. 2 is another, more detailed, schematic depiction of a hydraulicbrake system for an aircraft.

FIG. 3 is a schematic depiction of a shut-off valve for the hydraulicbrake system depicted in FIG. 2.

FIG. 4 is a graph depicting the relationship between master cylinderdisplaced volume and master cylinder pressure for the hydraulic brakesystem depicted in FIG. 2.

DETAILED DESCRIPTION

The descriptions and drawings herein are merely illustrative and variousmodifications and changes can be made in the structures disclosedwithout departing from the scope of the appended claims. Variousidentified components of a hydraulic system and a shut-off valvedisclosed herein are merely terms of art and may vary from onemanufacturer to another. The terms should not be deemed to limit thepresent disclosure or the appended claims. The drawings are shown forpurposes of illustrating one or more exemplary embodiments and are notfor purposes of limiting the appended claims. All references todirection and position, unless otherwise indicated, refer to theorientation of the components illustrated in the drawings and should notbe construed as limiting the appended claims.

FIG. 1 schematically depicts a hydraulic system 10 for an aircraft. Thehydraulic system 10 includes a master cylinder, and in the depictedexample, the hydraulic system 10 includes a pilot left-hand mastercylinder 12 a, a pilot right-hand master cylinder 12 b, a co-pilotleft-hand master cylinder 12 c, and a co-pilot right-hand mastercylinder 12 d. The hydraulic system 10 also includes a wheel brake,which in the depicted embodiment includes a left-hand wheel brake 14 aand a right-hand wheel brake 14 b. The hydraulic system 10 also includesa pressure supply 16, which can be an electrical motor driven hydraulicpump. The hydraulic system 10 also includes a reservoir 18, which can bea vented reservoir or tank or a pressurized reservoir or tank. Thehydraulic system 10 also includes a shut-off valve 20 that is incommunication with the master cylinders 12 a-12 d, the wheel brakes 14a, 14 b, the pressure supply 16 and the reservoir 18.

The pilot left-hand master cylinder 12 a is operated by a pilotleft-hand pedal 30 a. The pilot right-hand master cylinder 12 b isoperated by a pilot right-hand pedal 30 b. The co-pilot left-hand mastercylinder 12 c is operated by a co-pilot left-hand pedal 30 c. Theco-pilot right-hand master cylinder 12 d is operated by a co-pilotright-hand pedal 30 d.

A left-hand master cylinder outlet line 32 connects with the pilotleft-hand master cylinder 12 a. The left-hand master cylinder outletline 32 branches to connect with a brake valve supply line 34, which ismore particularly shown as a left-hand brake metering valve supply line34 in FIG. 2, which connects with a brake valve 110. As moreparticularly shown in FIG. 2, the brake valve 110 can include aleft-hand brake metering valve 36. The left-hand master cylinder outletline 32 also branches at a left-hand shut-off valve supply line 38 toconnect with a left-hand master cylinder port 40 a of the shut-off valve20. A right-hand master cylinder outlet line 42 connects with the pilotright-hand master cylinder 12 b. The right-hand master cylinder outletline 42 branches to connect with a brake valve supply line 44, which ismore particularly shown as a right-hand brake metering valve supply line44 in FIG. 2, which connects with the brake valve 110, which can includea right-hand brake metering valve 46 as shown in FIG. 2. The right-handmaster cylinder outlet line 42 also branches at a right-hand shut-offvalve supply line 48, which connects with a right-hand master cylinderport 40 b of the shut-off valve 20. A first connecting line 60 connectsthe co-pilot left-hand master cylinder 12 c to the pilot left-handmaster cylinder 12 a. Accordingly, upon actuation of the co-pilotleft-hand pedal 30 c, fluid exits the pilot left-hand master cylinder 12a through the left-hand master cylinder outlet line 32. Similarly, asecond connecting line 62 connects the co-pilot right-hand mastercylinder 12 d to the pilot right-hand master cylinder 12 b. A mastercylinder return line 64 also connects with the co-pilot left-hand mastercylinder 12 c and the co-pilot right-hand master cylinder 12 d, whichconnects the master cylinders to the reservoir 18.

A left-hand brake supply line 70 connects the left-hand brake 14 a tothe brake valve 110, which can also include an anti-skid control device72 as shown in FIG. 2. A right-hand brake supply line 74 connects theright-hand brake 14 b to the brake valve 110, which can also include theanti-skid control device 72 as shown in FIG. 2.

With reference to FIG. 2, both the left-hand brake 14 a and theright-hand brake 14 b connect with an emergency parking brake valve 76via a return line 78. The emergency parking brake valve 76 cancommunicate with the reservoir 18. A first hydraulic fuse 82 can beprovided on the left-hand brake supply line 70 between the anti-skidcontrol device 72 and the left-hand brake 14 a. A second hydraulic fuse84 can be provided on the right-hand brake supply line 74 between theanti-skid control valve 72 and the right-hand brake 14 b. The anti-skidcontrol valve 72 can be controlled by a brake control unit 86. Anelectrical line 88 can run between the anti-skid control valve 72 andthe brake control unit 86 to supply signals to the anti-skid controlvalve. A left-hand wheel speed transducer 94 a and a right-hand wheelspeed transducer 94 b can be provided for each respective wheel 96 a and96 b. A first electrical line 98 can connect between the brake controlunit 86 and the left-hand wheel speed transducer 94 a. A secondelectrical line 100 can connect the brake control unit 86 and theright-hand wheel speed transducer 94 b.

With continued reference to FIG. 2, the brake valve 110, which caninclude the left-hand brake metering valve 36, the right-hand brakemetering valve 46 and the anti-skid control valve 72, can also providehydraulic fluid via line 112 to landing gear 114 of the aircraft. Thebrake valve 110 and the hydraulic system 10 is more schematicallydepicted in FIG. 1 as compared to FIG. 1.

With reference back to FIG. 1, the brake shut-off valve 20 can include apressure supply port 120, which is connected to the pressure supply 16,a system pressure port, hereinafter referred to as a brake pressuresupply port 122, which is connected to the brake valve 110, and a returnport 124, which is connected to the reservoir 18. A return line 126 canconnect with a return port 128 of the brake valve 110 and the returnport 124 of the shut-off valve 20. With reference to FIG. 2, a checkvalve 130 can be provided between the return port 128 of the brake valve110 and the return port 124 of the shut-off valve 20 to block fluid flowfrom the return port 124 of the shut-off valve 20 toward the return port128 of the brake valve 110.

The shut-off valve 20 is operable in a first position, which blocksfluid flow between the pressure supply 16 and the wheel brakes 14 a, 14b through the shut-off valve 20. The shut-off valve 20 is also operablein a second position, which allows fluid flow between the pressuresupply 16 and the wheel brakes 14 a and 14 b through the shut-off valve20. Fluid pressure from the master cylinders 12 a, 12 b, 12 c and 12 dcontrols operation of the shut-off valve 20 between the first positionand the second position. As such, the pedals 30 a, 30 b, 30 c and 30 dand the master cylinders 12 a, 12 b, 12 c and 12 d can be referred to asa brake operation device. By using master cylinder pressure to open andclose the shut-off valve 20, hydraulic supply to the brake valve 110 canbe gradually increased according to the brake pedal movement. Thisgradual increase of hydraulic supply prevents hydraulic spikes andacoustic noise. By using master cylinder pressure to open and closepassages within the shut-off valve 20, partial strokes on the pedals 30a, 30 b, 30 c and 30 d can result in pressure being supplied from thepressure supply 16 toward the brakes 14 a and 14 b. In other words, thesecond position of the shut-off valve 20 need not supply unconstrainedor full fluid flow between the pressure supply 16 and the brake pressureport 122.

When the pedal 30 a or the pedal 30 c is pedaled, the shut-off valve 20moves into the second, open, position. When in the second position, thepressure to brake the left hand wheel 96 a is sourced from the pressuresupply 16 to the left hand wheel brake 14 a through the shut-off valve20, the left hand metering valve 36 and the anti-skid control valve 72.This brake force depends on the force on the pedal 30 a or 30 c. Theshut-off valve 20 moves back to the first position, which is closed, andthe left hand wheel 96 a is released by the left hand brake 14 a whenthe pedal 30 a or 30 c is not footed. Similarly, when the pedal 30 b orthe pedal 30 d is pedaled, the shut-off valve 20 moves into the secondposition. When in the second position, the pressure to brake the righthand wheel 96 b is sourced from the pressure supply 16 to the right handwheel brake 14 b through the shut-off valve 20, the right hand meteringvalve 46 and the anti-skid control valve 72. This brake force depends onthe force on the pedal 30 b or 30 d. The shut-off valve 20 moves back tothe first position, which is closed, and the right hand wheel 96 b isreleased by the right hand brake 14 b when the pedal 30 b or 30 d is notfooted.

With reference to FIG. 3, the shut-off valve 20 includes a housing 150including a bore 152. The bore 152 can formed in the housing 150 byboring or removing material from the housing 150 to provide a passagewaythrough which fluid can flow. Alternatively, the bore 152 can be formedin a casting operation such that a passage is formed through which fluidcan flow. The housing 150 further includes the master cylinder ports 40a and 40 b (one master cylinder port 40 is shown in FIG. 2), thepressure supply port 120, the brake pressure port 122, and the returnport 124. Each of the ports connects with the bore 152.

The shut-off valve 20 further includes a spool 154 disposed in the bore152. In the illustrated embodiment, the spool 154 is generally anelongate cylinder and includes an outer surface 156. A poppet 158 is onthe spool 154 and moves with the spool 154. In the illustratedembodiment, the poppet 158 includes a first (upper) valve face 162 and asecond (lower) valve face 164. The poppet 158 enlarges a portion of thespool 154 to selectively block flow of fluid through the bore 152 in amanner that will be described in more detail below. Movement of thepoppet 158 is controlled by operation of the brake operation device,e.g. the pedals 30 a, 30 b, 30 c and 30 d and the master cylinders 12 a,12 b, 12 c and 12 d. If desired, a mechanical linkage between the pedals30 a, 30 b, 30 c and 30 d and the shut-off valve 20 can be used insteadof the master cylinders 12 a, 12 b, 12 c and 12 d. This mechanicallinkage and the pedals 30 a, 30 b, 30 c and 30 d can also operate as thebrake operation device.

The shut-off valve 20 also includes a cap 170, which in the depictedembodiment is generally cylindrical in configuration. As illustrated inFIG. 3, the cap 170 fits inside an upper counterbore section 172 of thebore 152. The cap 170 includes a cylindrical central passage 174 thatreceives a portion of the spool 154. An inner cap seal 176 contacts thecap 170 and the spool 154 to prevent fluid flow from the bore 152 toambient. An outer cap seal 178 contacts the cap 170 and the housing 150to also prevent fluid flow between the bore 152 and ambient. The spool154 is movable within the passage 174 with respect to the cap 170 whilemaintaining a seal between the spool 154 and the cap 170 at the seal176.

The shut-off valve 20 further includes a first valve seat 182 disposedin the bore 152 between where the pressure supply port 120 connects withthe bore 152 and where the brake pressure port 122 connects with thebore 152. The first valve seat 182 can be an annular metal disc-shapedpiece that includes a central passage 184 that receives the spool 154.The first valve seat 182 is disposed in a valve seat section 186 of thebore 152 between where the pressure supply port 120 connects with thebore 152 and where the brake pressure port 122 connects with the bore152. The poppet 162 seals against the first valve seat 182 to blockfluid flow through the bore 152 from the pressure supply port 120 towardthe brake pressure port 122. More particularly, the first valve face 162of the poppet 158 seats against the first valve seat 182 to block thecentral passage 184 to block fluid flow through the bore 152 from thepressure supply port 120 toward the brake pressure port 122.

The shut-off valve 20 also includes a second valve seat 190, which canbe disposed in the valve seat section 186 of the bore 152. The secondvalve seat 190 can be an annular metal disc-shaped piece that includes acentral passage 192 that receives the spool 154. The second valve seat190 is disposed in the bore 152 between where the pressure supply port120 connects with bore and where the master cylinder port 40 connectswith the bore. Additionally, the second valve seat 190 is disposed inthe bore 152 between where the brake pressure port 122 connects withbore 152 and where the master cylinder port 40 connects with the bore152.

The poppet 158 is movable between a first position where the poppet 158acts against the first valve seat 182 and a second position where thepoppet 158 acts against the second valve seat 190. In the firstposition, fluid flow is blocked between the pressure supply 16 and thebrake valve 110 through the shut-off valve 20. In the second position,fluid flow is allowed between the pressure supply 16 and the brake valve110 through the shut-off valve 20. In the second position, fluid flow isalso blocked between the pressure supply 16 and the master cylinders 12a, 12 b, 12 c and 12 d. Speed of movement between the first position andthe second position is proportionate to an operation speed of the brakeoperation device, e.g., the pedals 30 a, 30 b, 30 c and 30 d and themaster cylinders 12 a, 12 b, 12 c and 12 d or the pedals 30 a, 30 b, 30c and 30 d and a mechanical linkage connected with the shut-off valve20.

The shut-off valve 20 also includes a seal 200 to preclude fluid flowbetween the pressure supply 16 (FIG. 1) and the reservoir 18 (FIG. 1)through to valve 20. The seal 200 cooperates with the spool 154 and thehousing 150 to block fluid flow through the bore 152 from the pressuresupply port 120 and the brake pressure port 122 toward the mastercylinder port 40. In the depicted embodiment, the seal 200 contacts thespool 154 and the housing 150 and is positioned below the second valveseat 190. The seal 200 can be an O-ring seal.

The shut-off valve 20 also includes an inner (first) piston 210 disposedin the bore 152 and connected with the spool 154 for movement with thespool 154. In the illustrated embodiment, the inner piston 210 includesa base 212, an upper extension 214, which extends away from the base 212in a first direction (toward the cap 170 in FIG. 3), and a lowerextension 216, which extends away from the base in a second direction.In the illustrated embodiment, the base 212 can be a generally circulardisc-shaped member. The outer diameter of the base 212 is larger thanthe outer diameter of the upper extension 214. The upper extension 214can be generally cylindrical in configuration and extend in a generallynormal direction from the base 212. The inner diameter of the upperextension 214 is larger than the outer diameter of the spool 154. Theouter diameter of the upper extension 214 and the inner diameter of theouter piston 230 are nearly the same. The lower extension 216 can alsobe generally cylindrical in configuration and include an inner surface224 and an outer surface 226. The lower extension 216 can also extend ina generally normal direction from the base 212. The inner diameter ofthe lower extension 216 and the outer diameter of the spool 154 arenearly the same.

The shut-off valve 20 also includes an outer (second) piston 230disposed in the bore 152. In the illustrated embodiment, the secondpiston 230 is generally cylindrical in configuration and includes asecond piston passage 232 that receives the upper extension 214 of firstpiston 210. The diameter of the base 212 of the first piston 210 islarger than the diameter of the second piston passage 232. In theillustrated embodiment, the first piston 210 cooperates with the secondpiston 230 to block fluid flow through the bore 152 from the mastercylinder port 40 toward the return port 124. The length of the upperextension 214 is longer than the length of the second piston passage 232such that movement of the first piston 210 relative to the second piston230 maintains sealing between the first piston 210 and the second piston230 through the second piston passage 232. Also, the second piston 230cooperates with the housing 150 to block fluid flow through the bore 150from the master cylinder port 40 toward the return port 124.

In the illustrated embodiment, the housing 150 includes a shoulder 234.A piston receiving section 236 of the bore 152 is defined below theshoulder 234 (per the orientation shown in FIG. 3). The outer diameterof the outer piston 230 and the outer diameter of the piston receivingsection 236 are nearly the same. The housing 150 also includes a returnline passage 238 that connects with the piston receiving section 236 ofthe bore 152 below the second piston 230 (per the orientation shown inFIG. 3) and the return port 124. An inner piston seal 242 contacts theinner piston 210 and the outer piston 230 to block fluid flow from themaster cylinder port 40 toward the return line port 124 (and morespecifically between the master cylinder port 40 and the return linepassage 238) through the bore 152. An outer piston seal 244 contacts theouter piston 230 and the housing 150 to block fluid flow between themaster cylinder port 40 and the return port 124 (and more specifically,the return line passage 238) through the bore 152.

The shut-off valve 20 also includes a first (inner) spring 250 biasingthe first piston 210 and the poppet 158 in a first direction toward thefirst valve seat 182. The inner spring 250 is disposed in the pistonreceiving section 236 of the bore 152. An inner spring retainer 252connects with the housing 150 to attach the inner spring 250 to thehousing 150. The inner spring 250 acts against the housing to bias thefirst piston 210 in the first direction. The inner diameter of the innerspring 250 is larger than the outer diameter of the lower extension 216and the outer diameter of the inner spring 250 is smaller than the outerdiameter of the base 212.

The shut-off valve 20 also includes a second (outer) spring 254 biasingthe second piston 230 in the first direction. The inner diameter of thepiston receiving section 236 is larger than the outer diameter of theouter spring 254. The outer spring 254 is also disposed within thepiston receiving section 236 of the bore 152. An outer spring retainer256 connects with the housing 150 to connect the outer spring 254 to thehousing 150. The outer spring retainer 256 includes a base 258, whichcan be generally annular, and an extension 260, which can becylindrical, that extends upwardly from the base 258 in the firstdirection. The outer diameter of the extension 260 is larger than theouter diameter of the base 212. The inner diameter of the outer spring254 is larger than the outer diameter of the extension 260. The shoulder234 retains the second piston 230 against the biasing force of the outerspring 254 so that the outer piston 230 does not travel to block themaster cylinder port 40. The outer spring retainer 256 is hollow andincludes a passage 262 that receives the inner piston 210 and the innerspring 250. The passage 262 has a diameter that is greater than thediameter of the base 212 of the inner piston 210, which allows the innerpiston 210 to travel within the passage 262 and be moveable with respectto the outer spring retainer 256. The upper extension 260 can also limitmovement of the outer piston 230 in a second direction, which isopposite the first direction, which is the direction in which the outerspring 254 biases the outer piston 230. The spool 154, the upperextension 214, the lower extension 216, the base 212, the inner spring250, the outer spring 254, the outer spring retainer 256, the base 258,the outer spring 230 and the piston receiving section 236 are disposedconcentrically. The inner spring 250, which is grounded in the innerspring retainer 252, biases the inner piston 210 toward the firstdirection. The outer spring 254, which is grounded in the base 258,biases the outer piston 230 toward the first direction.

Operation of the shut-off valve 20 will now be described in more detail.Normally, the first valve face 162 contacts the first valve seat 182,because the inner spring 250 biases the inner piston 210 and the spool154 toward the first direction. This is the closed condition of theshut-off valve 20. In the closed condition, the hydraulic fluid does notflow from the pressure supply port 120 to the brake pressure port 122.The shut-off valve 20 is designed such that fluid pressure at the mastercylinder port 40 overcomes the biasing force of the inner spring 250 anda return line pressure at the return port 124 to urge the poppet 158from the first valve seat 182 allowing fluid to flow through the bore152 from the pressure supply port 120 towards the brake pressure port122.

Fluid pressure from the master cylinder 12 a, 12 b, 12 c or 12 d entersthe shut-off valve 20 at the master cylinder port 40. The seal 200precludes fluid flow from the master cylinder port 40 toward thepressure supply port 120 and the brake pressure port 122. The innersurface 218 of the inner piston 210 is spaced from the outer surface 156of the spool 154 such that the fluid from the master cylinder port 40can enter between the inner surface 218 of the inner piston 210 and theouter surface 156 of the spool 154 to overcome the biasing force of theinner spring 250 and the return line pressure at the return port 124.The spool 154 and the inner piston 210 travel integrally. With the firstvalve face 162 unseated from the valve seat 182, fluid passes from thepressure supply port 120 through a pressure supply port passage 270 intothe bore 152, through the passage 184 in the valve seat 182 and into abrake pressure port passage 272, which is connected with the brakepressure port 122.

The stroke of the inner piston 210 is limited by the second valve face164 seating against the second valve seat 190. Volume compensation isaccomplished by movement of the outer piston 230 against the biasingforce of the outer spring 254 and the return port pressure at the returnport 124, because when the outer piston 230 moves down, inter spacebetween the outer piston 230 and the shoulder 234 enlarges. As seen inFIG. 3, the outer surface 222 of the inner piston 210 is spaced from theshoulder 234 such that fluid can enter the region of the bore 152 belowthe shoulder (per the orientation shown in FIG. 3). Accordingly, theouter piston 230 and the housing can operate as an accumulator (see FIG.2). When the force by the master cylinder pressure of the mastercylinder port 40 overtakes the force by the inner spring 250 and thereturn pressure of the return port 124, the spool 154 and the innerpiston 210 move integrally in a direction toward the second direction.At first, the second piston 230 does not move. When the force by themaster cylinder pressure of the master cylinder port 40 overtakes theforce by the inner spring 250, the outer spring 254 and the returnpressure of the return port, the spool 154, the inner piston 210 and theouter piston 230 move integrally in a direction toward the seconddirection. Thus, this mechanism realizes a volume compensator easily.The shut-off valve 20 gets into the open condition when the first valveface 162 moves away from the first valve seat 182 with a travel of thespool 154. Then, the hydraulic fluid flows from the pressure supply port120 to the brake pressure port 122. The stroke of the poppet 158 and theinner piston 210 are limited by the distance between the first valveseat 182 and the second valve seat 190.

A failure of the seal 200 results in fluid passing from the pressuresupply port 120 (and the brake pressure port 122) towards the mastercylinder port 40. Then, the pressure in the master cylinder port 40increases and the second valve face 164 of the poppet 158 moves towardthe second valve seat 190. When the second valve face 164 seats againstthe second valve seat 190, further fluid flow from the brake pressuresupply port 120 and the brake pressure port 122 toward the mastercylinder port 40 is blocked. Failure of the seal 200 can result inuncommanded application of x % of the brake pressure at the left-handbrake 14 a (FIG. 1) and the right-hand brake 14 b (FIG. 1). In oneexample x % can be at least about 70% of a maximum brake pressure ineach wheel brake 14 a, 14 b. The brake pressure increases until thesecond valve face 164 contacts the second valve seat 190. In thishydraulic brake system, up to the 70% of the brake pressure at the brake14 a, 14 b is provided until the second valve face 164 contacts thesecond valve seat 190 without brake pedal operation by the pilots. Toreiterate, in this embodiment, the value 70% is merely an example. Thispercentage is decided in response to the distance between the secondvalve face 164 and the second valve seat 190, the spring force of theinner spring 250 and the like. Therefore, the percentage of the brakepressure is decided for each hydraulic brake system. If the seal 200fails, the pilot of the aircraft is then able to control braking from70% to 100% by pedal the brake pedals. If the distance between thesecond valve face 164 and the second valve seat 190, the spring force ofthe inner spring 250 or the like were modified, then the pilot of theaircraft would be able to control braking from x % (depending on themodifications) to 100% of maximum brake pressure upon failure of theseal 182. If the pressure in the pressure supply port 120 continued toflow into the master cylinder port 40, as in other designs, theunintended full brake condition might have occurred, which isundesirable. Since the second valve seat 190 is made of metal in theillustrated embodiment, the failure of the metal-to-metal contactbetween the second valve face 164 and the second valve seat 190 isunlikely. The failure of both the valve seat 190 and the seal 200 ishighly unlikely due to the nature of a metal-to-metal seal between thesecond valve face 164 and the second valve seat 190.

FIG. 4 depicts the relationship between master cylinder 12 a, 12 b, 12 cor 12 d displaced volume and master cylinder pressure. The solid line300 on the graph denotes the relationship between master cylinder 12 a,12 b, 12 c or 12 d displaced volume and master cylinder pressure uponfailure of the seal 200, and the diamond-dotted line 302 denotes therelationship between master cylinder 12 a, 12 b, 12 c or 12 d displacedvolume and master cylinder pressure when the seal 200 has not failed.The portions 300 a, 302 a of each line 300, 302, respectively, having alesser slope denotes when the piston 230 (FIG. 3) moves to accommodatefluid from the master cylinder 12 a, 12 b, 12 c or 12 d duringadditional displacement of the pedal 30 a, 30 b, 30 c or 30 d after thepoppet 158, and more particularly the valve face 164, contacts the valveseat 190. The respective points 300 b, 302 b where each line 300, 302,respectively, changes slope denotes when the poppet 158, and moreparticularly the valve face 164, contacts the valve seat 190. Thedistance between the points 300 b, 302 b where each line 300, 302,respectively, changes slope and the maximum displaced volume 300 c, 302c (about 680 psig in FIG. 4) denotes the percentage of maximum brakepressure in the wheel brake 14 a, 14 b after the poppet 158, and moreparticularly the valve face 164, contacts the valve seat 190. As such,as seen when viewing line 300, and more particularly portion 300 a, thepilot can operate the wheel brakes 14 a, 14 b between x %, e.g. 70%, ofmaximum pressure and 100% of maximum pressure after the seal 200 (FIG.3) has failed and the popper 158 is seated against the valve seat 190.

A method for operating a brake system can includes depressing the pedal30 a, 30 b, 30 c or 30 d to move the poppet 158 in a shut-off valve 20from a first position toward a second position. When in the firstposition the poppet 158 blocks fluid flow between the pressure source 16and the brake valve 120. When in the second position the poppet 158 ispositioned to allow fluid flow between the pressure source 16 and thebrake valve 110. The wheel brake 14 a or 14 b, which is connected withthe shut-off valve 20, is at x % of a maximum brake pressure when thepoppet 158 is in the second position. The method further includesfurther depressing the pedal 30 a, 30 b, 30 c or 30 d with the poppet158 in the second position to provide a brake pressure greater than x %in the wheel brake 14 a or 14 b. Depressing the pedal 30 a, 30 b, 30 cor 30 d moves fluid from the master cylinder 12 a, 12 b, 12 c or 12 dtowards the shut-off valve 20. Further depressing the pedal 30 a, 30 b,30 c or 30 d moves fluid from the master cylinder 12 a, 12 b, 12 c or 12d to displace the piston 230 in the shut-off valve 20. Furtherdepressing the pedal 30 a, 30 b, 30 c or 30 d also moves fluid from themaster cylinder 12 a, 12 b, 12 c or 12 d toward the brake valve 110,which can include at least one of a metering valve 36, 46 and ananti-skid valve 72 disposed downstream from the shut-off valve 20. Aspeed at which the poppet 158 moves from the first position toward thesecond position is proportionate to an operation speed at which thepedal 30 a, 30 b, 30 c or 30 d is depressed.

A hydraulic system for an aircraft and a shut-off valve for such ahydraulic system have been described above with particularity.Modifications and alterations will occur to those upon reading andunderstanding the preceding detailed description. The appended claimsare not to be limited only to the embodiment described above.

It will be appreciated that various of the above-disclosed and otherfeatures and functions, or alternatives or varieties thereof, may bedesirably combined into many other different systems or applications.Also that various presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art which are also intended to beencompassed by the following claims.

1. A hydraulic system for an aircraft comprising: a brake operationdevice; a pressure supply; a reservoir; a brake valve; a shut-off valvein fluid communication with and disposed between the pressure supply andthe brake valve, the shut-off valve including a poppet, a first valveseat and a second valve seat each positioned in the shut-off valve,wherein movement of the poppet is controlled by operation of the brakeoperation device, wherein the poppet is movable between a first positionwhere the poppet acts against the first valve seat and a second positionwhere the poppet acts against the second valve seat, in the firstposition fluid flow is blocked between the pressure supply and the brakevalve through the shut-off valve, in the second position fluid flow isallowed between the pressure supply and the brake valve through theshut-off valve; and a wheel brake in fluid communication with anddownstream from the shut-off valve, wherein the wheel brake operates ata maximum fluid pressure and the wheel brake is at x % of the maximumpressure when the poppet is in the second position, where x %<100%. 2.The system of claim 1, wherein a speed of movement between the firstposition and the second position is proportionate to an operation speedof the brake operation device.
 3. The system of claim 1, wherein thebrake operation device includes a master cylinder and a pedal, whereinthe master cylinder is in fluid communication with the shut-off valve.4. The system of claim 3, wherein with the poppet in the second positionfluid flow is blocked between the pressure supply and the mastercylinder.
 5. The system of claim 1, wherein the brake valve includes atleast one of a brake metering valve and an anti-skid valve.
 6. Thesystem of claim 1, wherein the wheel brake is at least about 70% of themaximum pressure when the poppet is in the second position.
 7. Thesystem of claim 1, wherein additional displacement of the brakeoperation device with the poppet in the second position results in brakepressures greater than x % up to 100% of the maximum brake pressure inthe wheel brake.
 8. The system of claim 7, wherein x % is a function ofa distance between the poppet and the second valve seat when the poppetis in the first position.
 9. The system of claim 8, further comprising aspring biasing the poppet towards the first position, wherein x % isalso a function of a biasing force of the spring.
 10. The system ofclaim 7, wherein the brake operation device includes a master cylinderand a pedal, wherein the master cylinder is in fluid communication withthe shut-off valve, wherein the shut-off valve includes a piston whichdisplaces in the shut-off valve when the poppet is in the secondposition to accommodate fluid from the master cylinder during additionaldisplacement of the pedal after the poppet is in the second position.11. A method for operating a brake system comprising: depressing a pedalto move a poppet in a shut-off valve from a first position toward asecond position, when in the first position the poppet blocks fluid flowbetween a pressure source and a brake valve and when in the secondposition the poppet allows fluid flow between the pressure source andthe brake valve, wherein a wheel brake connected with the shut-off valveis at x % of a maximum brake pressure when the poppet is in the secondposition; and further depressing the pedal with the poppet in the secondposition to provide a brake pressure greater than x % in the wheelbrake.
 12. The method of claim 11, wherein depressing the pedal movesfluid from a master cylinder towards the shut-off valve.
 13. The methodof claim 11, wherein further depressing the pedal moves fluid from amaster cylinder to displace a piston in the shut-off valve.
 14. Themethod of claim 13, wherein further depressing the pedal also movesfluid from the master cylinder toward the brake valve, which is at leastone of a metering valve and an anti-skid valve disposed downstream fromthe shut-off valve.
 15. The method of claim 11, wherein a speed at whichthe poppet moves from the first position toward the second position isproportionate to an operation speed at which the pedal is depressed. 16.A shut-off valve comprising: a housing including a bore, a mastercylinder port, a pressure supply port, a system pressure port, and areturn port, wherein each port connects with the bore and the boreincludes a valve seat section and a piston receiving section, whereinthe valve seat section is connected with the system pressure port,wherein the piston receiving section is connected with the return port;a first valve seat disposed in the valve seat section of the borebetween the pressure supply port and the system pressure port; a secondvalve seat disposed in the valve seat section of the bore between thesystem pressure port and the master cylinder port; a spool disposed inthe bore; a poppet on the spool, wherein the poppet moves with the spooland is disposed in the valve seat section for movement between the firstvalve seat and the second valve seat; a first piston disposed in thepiston receiving section of the bore and connected with the spool formovement with the spool; and a first spring disposed in the pistonreceiving section of the bore and biasing the first piston and thepoppet in a first direction towards the first valve seat, wherein whenpressure at the master cylinder port overcomes a biasing force of thefirst spring and pressure at the return port the first piston and thepoppet travel in a second direction.
 17. The shut-off valve of claim 16,further comprising a seal between the second valve seat and the mastercylinder port, wherein the seal cooperates with the spool and thehousing to block fluid flow through the bore from the pressure supplyport and the system pressure port toward the master cylinder port. 18.The shut-off valve of claim 16, further comprising a second piston and asecond spring each disposed in the piston receiving section of the boreand, the second piston including a second piston passage that receivesthe first piston, the second spring biasing the second piston in thefirst direction, the second piston travels with the first piston and thespool toward the second direction when the pressure at the mastercylinder port is larger than a total force of the first spring, thesecond spring and pressure at the return port.
 19. The shut-off valve ofclaim 16, wherein the first piston includes a first extension and asecond extension extending in opposite directions from a base, whereinan inner diameter of the first extension is larger than an outerdiameter of the spool and a space between the inner diameter of thefirst extension and the outer diameter of the spool is connected withthe master cylinder port.
 20. The shut-off valve of claim 16, furthercomprising an inner piston seal disposed between the first piston andthe second piston and an outer piston seal disposed between the secondpiston and the housing.
 21. A hydraulic system for an aircraftcomprising: a master cylinder; a wheel brake; a pressure supply; areservoir; and a shut-off valve in communication with the mastercylinder, the wheel brake, the pressure supply and the reservoir, theshut-off valve including a bore having a valve seat section and a pistonreceiving section, wherein the valve seat section is connected with thewheel brake, wherein the piston receiving section is connected with thereservoir; a first and second valve seats disposed in the valve seatsection of the bore; a spool disposed in the bore; a poppet on thespool, wherein the poppet moves with the spool and is disposed in thevalve seat section for movement between the first valve seat and thesecond valve seat; a first piston disposed in the piston receivingsection of the bore and connected with the spool for movement with thespool; and a first spring disposed in the piston receiving section ofthe bore and biasing the first piston and the poppet in a firstdirection towards the first valve seat, when the poppet seals againstthe first valve seat fluid flow from the pressure supply to the wheelbrake is blocked, wherein when pressure from the master cylinderovercomes a biasing force of the first spring and pressure at a returnport connected with the reservoir the first piston and the poppet travelin a second direction away from the first valve seat.